This invention concerns the preparation of polymers with low polydispersity and/or controlled molecular weight and architecture by the use of living free radical polymerization initiated by an alkoxyamine or an appropriate nitroxide-initiator combination It also concerns novel compounds useful in such polymernzations and methods for their preparation.
Living radical polymerization based on the use of alkoxyamine initiators was invented by Rizzardo et al and is described in U.S. Pat. No. 4,581,429. Recent publications by Georges et al (Trends Polym. Sci., 1994, 2, 66-72), Hawker (J. Am. Chem. Soc., 1994, 116, 11185-11186) and others have described the application of the methodology to the synthesis of narrow polydispersity polystyrenes. The nitroxide component in these latter studies is most often 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or one of its derivatives. We have now discovered the advantages of nitroxide-mediated living free-radical polymerizations employing imidazoline nitroxides (1) as further defined hereafter: 
The characteristics of a living polymerization are discussed by Quirk and Lee (Polymer International 27, 359 (1992)) who give the following experimentally observable criteria:
1. Polymerization proceeds until all of the monomer has been consumed. Further addition of monomer results in continued polymerization.
2. The number average molecular weight (or the number average degree of polymerization) is a linear function of conversion.
3. The number of polymer molecules (and active centers) is a constant which is sensibly independent of conversion.
4. The molecular weight can be controlled by the stoichiometry of the reaction.
5. Narrow molecular weight distribution polymers are produced.
6. Block copolymers can be prepared by sequential monomer addition.
7. Chain end-functionalized polymers can be prepared in quantitative yield.
This invention provides a polymer of the Formula (2) below: 
wherein:
R, R1, R2, R3 are each independently selected from the group consisting of C1 to C18 alkyl, substituted C1 to C18 alkyl, C6 to C18 aryl, C6 to C18 substituted aryl; R groups that are in a geminal position with respect to each other can together form a 4-8 membered ring; R groups that are in a cis position with respect to each other can together form a 4-8 membered ring;
X is selected from the group consisting of hydrogen, C1 to C18 alkyl, substituted C1 to C18 alkyl, C6 to C18 aryl, C6 to C18 substituted aryl; acyl; X and R can form a 5-8 membered ring; X and R3 can form a 5-8 membered ring;
M is one or more monomer units selected from the group consisting of styrene, substituted styrene, alkyl acrylate, alkyl methacrylate, substituted alkyl acrylate, substituted alkyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-allcylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide, N,N-dialkylmethacrylamide, isoprene and butadiene; n is an integer greater than 1;
Y is a residue derived from a species that initiates free radical polymerization or is selected from the group consisting of C1 to C18 alkyl, substituted C1 to C18 alkyl, C1 to C18 alkoxy, substituted C1 to C18 alkoxy, C6 to C18 aryl, C6 to C18 substituted aryl, C6 to C18 aryloxy, C6 to C18 substituted aryloxy, (C1 to C18 alkoxy)carbonyloxy, (C6 to C18 aryloxy)carbonyloxy, and sulfate radical anions; and
all substituents are independently selected from the group that consists of epoxy, hydroxy, C1 to C18 alkoxy, acyl, acyloxy, alkoxycarbonyl, aryloxycarbonyl, cyano, silyl, halo, and C1 to C18 dialkylamino.
The polymers of this invention have low polydispersity which provide improved flow properties in melt or solution. In addition, the presence of the mirroxyl end-group allows the formation of block copolymers by heating the preformed polymer with a different monomer. Alternatively, the Mitroxyl end-group can be reduced or chemically modified to give a polymer with a more desirable end-group. The term xe2x80x9cpolymer(s)xe2x80x9d employed herein includes block and graft copolymers and other complex architectures.
Specific monomers or comonomers from which M is derivable include the following:
methyl methacrylate, ethyl methacrylate, propyl methacrylate (all isomers), butyl methacrylate (all isomers), 2-ethylhexyl methacrylate, isobornyl methacrylate, methacrylic acid, benzyl methacrylate, phenyl methacrylate, methacrylonitrile, alpha-methylstyrene, methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate, isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate, acrylonitrile, styrene, functional methacrylates, acrylates and styrenes selected from glycidyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate (all isomers), hydroxybutyl methacrylate (all isomers), N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, triethyleneglycol methacrylate, itaconic anhydride, itaconic acid, glycidyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate (all isomers), hydroxybutyl acrylate (all isomers), N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate, triethyleneglycol acrylate, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-tert-butylmethacrylamide, N-n-butylmethacrylamide, N-methylolmethacrylamide, N-ethylolmethacrylamide, N-tert-butylacrylamide, N-n-butylacrylamide, N-methylolacrylamide, N-ethylolacrylamide, vinyl benzoic acid (all isomers), diethylaminostyrene (all isomers), alpha-methylvinyl benzoic acid (all isomers), diethylamino alpha-methylstyrene (all isomers). p-vinylbenzene sulfonic acid, p-vinylbenzene sulfonic sodiun salt, trimethylsilylpropyl methacrylate, trimethylsilylpropyl methacrylate, tributoxysilylpropyl methacrylate, dimethoxymethylsilylpropyl methacrylate, diethoxymethyl-silylpropylmethacrylate, dibutoxymethylsilylpropyl methacrylate, diisopropoxymethylsilylpropyl methacrylate, dimethoxysilylpropyl methacrylate, diethoxysilylpropyl methacrylate, dibutoxysilylpropyl methacrylate, diisopropoxysilylpropyl methacrylate, trimethylsilylpropyl acrylate, trimethylsilylpropyl acrylate, tributoxysilylpropyl acrylate, dimethoxymethylsilylpropyl acrylate, dimethoxymethylsilylpropyl acrylate, dibutoxymethylsilylpropyl acrylate, diisopropoxymethylsilylpropyl acrylate, dimethoxysilylpropyl acrylate, diethoxysilylpropyl acrylate, dibutoxysilylpropyl acrylate, diisopropoxysilylpropyl acrylate, maleic anhydride, N-phenylmaleimide, N-burylmaleimide, butadiene, isoprene, chloroprene.
This invention provides a process for preparing the polymers of Formula (2) comprising contacting reactant (i) with one or both of reactants (ii) and (iii) wherein.
(i) is at least one monomer M;
(ii) is at least one imidazoline nitroxide of the formula 
xe2x80x83and a source of free radicals Yxe2x80xa2; and
(iii) is at least one alioxysmine selected from the formula 
xe2x80x83wherein:
R, R1, R2, R3, X, M and Y are defined above;
Z is a group having at least one carbon atom such that the carbon centered radical Z xe2x80xa2 is capable of initiating free-radical polymerization of monomer (M); Y and the reaction conditions are selected so that the Y(M)nxe2x80x94O moiety in the compounds of Formula (2) formed from reactants (i) and (ii) undergo facile homolysis; Z and the reaction conditions are selected so that the Z-O moiety and the Z(M)nxe2x80x94O moiety formed by reacting (i) with (iii) undergo facile homolysis; n is an integer of 1 or greater; and Yxe2x80xa2 can be produced thermally from the monomer (when one of the monomers is styrene or a styrene derivative) or from a free-radical initiator or combination of initiators.
Use of the nitroxides of Formula 1 (or the corresponding alkoxyamines) offers significant advantages over nitroxides previously employed in nitroxide-mediated polymerization: homopolymers, statistical copolymers and block copolymers which have controlled molecular weight, a narrow molecular weight distribution and a defined end-group functionality can be synthesized. The method is also adaptable to the preparation of multi-block and graft and other polymers of more complex architecture. With appropriate selection of the substituents, R, R1, R2, R3, and X, (defined hereafter), the use of the nitroxides (1) offers lower polydispersities and better living character than, for example, TEMPO and derivatives.
Further advantages are that (a) the nitroxides (1) and the derived alkoxyamines are synthesized from readily available precursors by a simple experimental route; (b) they are subject to fewer side reactions (e.g., disproportionation of propagating radical with nitroxide or chain transfer to nitroxide); and (c) they are involatile. This provides an advantage over many of the most commonly used nitroxides such as TEMPO and many of its derivatives, and di-t-butyl nitroxide, which are odorous.
The process can be run continuously or in batch and can be carried out as a solution, emulsion, suspension or bulk polymerization using procedures well known in the art.
If Z is a polymer chain (e.g., Y(M)nxe2x80x94) then the product can be a block copolymer. Block copolymers can also be prepared by the sequential addition of different monomers or monomer combinations. Graft copolymers and polymers of more complex architecture can be prepared from appropriately designed precursors containing multiple nitroxide moieties.
Polymerization reaction conditions include temperatures in the range of about 20xc2x0 C. to 300xc2x0 C., preferably between 40xc2x0 C. to 250xc2x0 C., and most preferably between 50xc2x0 C. to 150xc2x0 C., ambient pressures up to 100 atmospheres and optional solvent(s) compatible with the monomer/polymer systems.
The polymers made by the process in this invention are also characterized by possessing functional end groups which are derived from the moieties Y and/or Z and the nitroxide fragment (1). Such functionality will include hydroxy; carboxylic acid (xe2x80x94COOH) and its esters; cyano; isocyanato; epoxy; halo; amino; and the like.
This invention concerns particular nitroxides of the Formula (1) useful in the polymerization process wherein:
R, R1, R2, R3 arc each independently selected from the group consisting of C1 to C18 alkyl, substituted C1 to C18 alkyl, C6 to C18 aryl, C1 to C18 substituted aryl; R groups in a geminal position with respect to each other can together form a 4-8 membered ring; and R groups in a cis position with respect to each other can together form a 4-8 membered ring; and
X is selected from the group consisting of C1 to C18 alkyl, substituted C1 to C18 alkyl, C6 to C18 aryl, C6 to Car substituted aryl; acyl; X and R can form a 5-8 membered ring; and X and R3 can form a 5-8 membered ring; with the proviso that R, R1, R2, R3 and X are not all methyl.
Preferred nitroxides selected from the group above are the following: 
where X is selected from the group consisting of alkyl, optionally substituted alkyl, benzyl; and 
where X is alkyl of C1 to C18.
This invention also concerns novel alkoxyamines of the Formula (3) wherein:
R, R1, R2, R1 are each independently selected from the group consisting of C1 to C18 alkyl, substituted C1 to C18 alkyl, C6 to C18 aryl, C6 to C18 substituted aryl; R groups in a germinal position with respect to each other can together form a 4-8 membered ring, and R groups in a cis position with respect to each other can together form a 4-8 membered ring;
X is selected from the group consisting of hydrogen, C1 to C18 alkyl, substituted C1 to C18 alkyl, C6 to C18 aryl, C6 to C18 substituted aryl; acyl; X and R can form a 5-8 membered ring; and X and R3 can form a 5-8 membered ring; and
Z is a group having at least one carbon atom and the carbon centered radical Zxe2x80xa2 is capable of initiating free radical polymerization of the monomer (M).
Suitable Z groups are xe2x80x94C(Me)2Ph, xe2x80x94C(Me)CN, xe2x80x94C(Me)(CN) CH2CH(Me)2, xe2x80x94C(Me)(CN)(substituted alkyl), xe2x80x94C(Me)2CO2Alkyl, xe2x80x94C(Me)2CO2H, xe2x80x94C(Me)2CH2C(Me)3, xe2x80x94C(Me)3, xe2x80x94C(Me)HPh and Y(M)nxe2x80x94.
This invention also includes a process for making the nitroxides of Formula (1). The process comprises reacting an aminonitrile and a ketone to form a cyanouimne, and reacting said imine with hydrogen sulfide to produce a linear thioamide, and cyclizing said linear thioamide to form a 2,2,5,5,-tetrasubstitute-dimidazolidin-4-thione, and converting the cyclic thioamide to the corresponding cyclic amide and then converting the final imidazolidine-4-one to the nitroxide.
In particular, the process for making nitroxides of Formula (1) involves: (i) preparing a colorless aqueous ammonium sulfide solution containing sodium thiocyanate by titrating an aqueous ammonium sulfide solution containing ammonium polysulfide with sodium cyanide under nitrogen; (ii) sequentially adding an aminonitrile and a ketone to the aqueous ammonium sulfide solution under nitrogen; (iii) adding base and then neutralizing; and (iv) oxidizing the reaction product of step (iii) to form the nitroxide.
Alternatively, in process step (ii) aminonitrile can be replaced by a mixture of ketone, ammonium chloride, and sodium or potassium cyanide. In another embodiment of this process the process is stopped before addition of sodium rungstate and the corresponding cyclic amine/amide is isolated. Process step vii) can be performed at a temperature of between 20xc2x0 and 80xc2x0 C., preferably between 30xc2x0 and 60xc2x0 C., and most preferably at 54xc2x0 C. The base is preferably sodium carbonate or sodium hydroxide, most preferably sodium hydroxide. Any convenient acid can be used for the neutralization, the preferred acid is sulfuric acid. In this process, the concentration of hydrogen peroxide is preferably 20 to 50%, most preferably 30%. The preferred oxidants for the amine to nitroxide transformation are H2O2/tungstate, dimethyldioxirane, H2O2/acetic acid.
The most commonly used nitroxides in nitroxide-mediated living free-radical polymerizations have been 2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO) and derivatives of this compound and di-t-butyl nitroxide (diBuNO). 
These and other nitroxides/alkoxyamines that are conventionally used in nitroxide-mediated living free-radical polymerizations are inherently of high cost Substantial cost improvements for the overall process can therefore be achieved by the use of nitroxide (1), a material obtainable from inexpensive precursor by a simple experimental route.
It has been found, that in various polymerizations, the use of certain 2,2,5,5-tetraalkylimidazolin-4-one-1-oxyl derivatives in nitroxide-mediated polymerization offer lower polydispersities for polymers than is obtained with other nitroxides used for this purpose (e.g., TEMPO and derivatives, or diBuNO).
In the context of the present invention, low polydispersity polymers are those with polydispersities that are significantly less than those produced by conventional free radical polymerization. In conventional free radical polymerization, polydispersities (the polydispersity is defined as the ratio of the weight average and number average molecular weights xe2x80x94Mw/{overscore (M)}n) of the polymers formed are typically in the range 1.6-2.0 for low conversions ( less than 10%) and can be substantially greater than this for higher conversions. Polydispersities obtained with the present invention are usually less than 1.5, often less than 1.3 and, with appropriate choice of the nitroxides (1)/alkoxyamines and the reaction conditions, can be less than 1.1. The low polydispersity can be maintained at high conversions.
Polydispersities in nitroxide-mediated polymerization are believed to depend on a number of factors. These include (i) the rate of exchange between active and dormant species which is largely determined by the rate of bond homolysis between Nxe2x80x94O and the adjacent moiety for the alkoxyamines involved either as initiator species or formed during the polymerization (for a discussion on this subject see Moad and Rizzardo, Macromolecules 1995, 28, 8722-8); and (ii) the significance of various side reactions.
For polymerizations involving nitroxides (1) the rate of bond homolysis between Nxe2x80x94O and the adjacent moiety and polydispersities obtained depend on the particular nitroxide or alkoxyamine used and in particular on the substituents R, R1, R2, R3and X. A preferred group of nitroxides in this context are the N-alkyl-2,2,5,5-tetraalkylimidazolin-4-one-1-oxyl compounds (i.e., (1) X=alkyl, for example, 2,5-bis(spirocyclohexyl)-3-methylimidazolidin-4-one-1-oxyl (NO-88-Me)) which are seen to offer the lowest polydispersities in styrene polymerizations or copolymerizations. Also preferred within each class (X=alkyl and X=H) are those (1) with more bulky R-R3.
The following are structures of nitroxides described herein: 
It is believed that an important side reaction in nitroxide-mediated polymerization is disproportionation between the nitroxide and the propagating species. It has been found that in methyl methacrylate (MMA) polymerization the use of 2,2,5,5-tetraalkylimidazolin-4-one-1-oxyl derivatives offer low polydispersities and good living character for polymerizations.
While not wishing to be bound by a particular mechanism, these advantages are believed to be in part a consequence of the 5-membered ring imidazoline nitroxides providing a higher combination: disproportionation ratio for the reaction with propagating radicals than 6-membered ring (i.e., TEMPO) or open chain nitroxides (i.e., diBuNO). These pathways are illustrated in Scheme 1 for MMA polymerization Note that the products of the disproportionation reaction, vinyl terminated macromonomer and hydroxylamine (H-Q) can also react further under polymerization reaction conditions leading to further complications. Clearly, minimization of this side reaction is important to obtaining polymerization with living characteristics. 
In Scheme 1, Q is a nitroxide.
Similar side reactions have also been shown to occur during nitroxide-mediated styrene polymerization. In styrene polymerization at 90xc2x0 C., the rate constants for hydrogen transfer from the propagating species to NO-67 and TEMPO relative to the rate constant of propagation have been measured as 0.18 and 0.43 respectively.
In the synthesis of nitroxides of Formula (1), the product nitroxide can be isolated by conventional means, preferably from the reaction mixture by filtration or by extraction with an organic solvent that is substantially insoluble in water.
It has been found that the ammonium polysulfide reacts with either aminonitrile or cyanide ion, thereby reducing the amount of cyanide below stoichiometric proportions thus lowering the overall yield. This can be prevented by prior addition of cyanide ion to the point of decolorization of the polysulfide and formation of harmless thiocyanate.
The procedure disclosed herein for synthesis of nitroxides (1, X=H) is as follows: 
The alkoxyamines of this invention are made from the compounds of Formula (1) by combining them with Zxe2x80xa2 for example by the procedure of Example 43 and by that described in Macromolecules, 1997, 30, 6445-6450. The alkoxyamines of this invention can be made by a variety of methods such as alkylating the derived hydroxylamines of nitroxides of Formula (1); and alkoxylating the compound of Formula (6) as will be obvious to one skilled in the art.